Apparatus and method for transmission power balance adjustment in a mobile cellular system

ABSTRACT

A transmission power control system can establish synchronization by matching adjustment start timings while repeating adjustment periods even when start timings of transmission power balance adjustment are different due to fluctuation of transmission delay of control message from the control station to base station, and can increase circuit capacity by establishing balance of transmission powers between the base stations. In the transmission power control system the base station comprises control means for controlling initiation of a balance adjustment period for performing the balance adjustment from a frame number determined on the basis of frame number of the balance adjustment period.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of co-pending U.S. patentapplication Ser. No. 11/904,068, filed on Sep. 26, 2007, which is acontinuation, and claims benefit under 35 U.S.C. §120, of co-pendingU.S. patent application Ser. No. 11/214,322, filed on Aug. 29, 2005,which is a continuation of U.S. Pat. No. 6,978,150 filed on Jun. 25,2001 and issued Dec. 20, 2005, which claims priority under 35 U.S.C. §119 of Japanese Patent Application Number 2000-198059, filed 25 Jun.2000, the complete disclosures of which are hereby incorporated byreference in their entirety for all purposes.

BACKGROUND OF THE INVENTION

1. Field of Invention

The present invention relates generally to a transmission power controlsystem, a control method, a base station and a control station and astorage medium recording a control program. More particularly, theinvention relates to a method for determining a balance adjustment starttiming upon performing balance adjustment of a transmission power forone mobile station from a plurality of base stations at the occurrenceof soft hand-over in cellular communication system.

2. Description of Related Art

In a code division multiplex cellular system, a plurality of channelsuse the same frequency, a reception power (desired wave power) of asignal at certain channel becomes an interference wave power to bejamming for other channels. Accordingly, in an uplink transmitted from amobile station to a base station, when the desired wave power is greaterthan or equal to a predetermined value, interference wave power isincreased to reduce capacity of the channel. In order to prevent this,it becomes necessary to strictly control the transmission power of themobile station. The transmission power control in the uplink isperformed in such a manner that the base station measures the desiredwave power to compare with a target control value for transmitting a upcontrol instruction for reducing a transmission power (hereinafterreferred to as “up transmission power”) of the uplink for the mobilestation when the desired power is larger than the target control value,and for transmitting the up control instruction for increasing the uptransmission power for the mobile station when the desired wave power issmaller than the target control value. Then, the mobile stationincreases or decreases the up transmission power according to the upcontrol instruction. Transmission of the up control instruction in thetransmission power control is performed using a downlink transmittingfrom the base station to the mobile station.

On the other hand, even in the downlink, by performing transmissionpower control so that a ratio between the desired wave power and theinterference wave power becomes a predetermined amount to realize highchannel capacity. In greater detail, in the transmission power controlin the downlink, the mobile station measures a reception quality of thedownlink to compare with a target control value for transmitting a downcontrol instruction for reducing transmission power of the downlink(hereinafter referred to as “down transmission power”) for the basestation when the reception quality is higher than the target controlvalue, and for transmitting down control instruction for increasing thedown control power when the reception quality is lower than the targetcontrol value. Then, the base station increases or decreases the downtransmission power according to the down control instruction.

However, in this method, when propagation loss from the mobile stationto the base station is abruptly increased associating with movement ofposition of the mobile station, the base station cannot receive the downcontrol instruction from the mobile station. At the same time, even inthe mobile station, it can become impossible to receive the up controlinstruction from the base station. At this time, in the conventionalmethod for only controlling transmission power of the downlink in themobile station by down control instruction from the base station, when acondition where the propagation loss is increased, is continued, whilethe base station cannot receive the down control instruction from themobile station, the base station does not increase the transmissionpower of the downlink. Therefore, even in the mobile station, it becomesimpossible to receive the up control instruction from the base station.Thus, the up transmission power of the signal in the uplink is notincreased to continue a condition where communication between the mobilestation and the base station is interrupted.

On the other hand, in general, among signals received by the basestation, a portion of user information, such as voice, data and so forthare encoded in such a manner that information having relatively longdata length are encoded in a lump so that they can be accurately decodedby performing error correction and so forth even when reception error ina moment is caused. Even upon decoding, information having long datalength can be decoded in a lump over a relatively long period.

However, during movement of the mobile station at high speed, when highspeed transmission power control is performed for maintaining areception quality constant following to high speed fading fluctuation inthe propagation path, even if the user information can be decodedaccurately, judgment of the control instruction has to be performed in amoment. Effect of error correction and so forth cannot be obtained injudgment of the control instruction to contain error relativelyfrequently.

Since error in judgment of such control instruction is caused inrelation to increase and decrease of propagation loss, possibility ofcontinuously causing propagation loss becomes relatively high. Then,when judgment error of the control instruction is continuously caused,the base station cannot control the down transmission power of thesignal in the downlink according to the down control instruction fromthe mobile station to make it impossible to accurately receive thesignal in the downlink in the mobile station. On the other hand, in thiscondition, even in the mobile station, since the up control instructionfrom the base station contained in the signal of downlink cannotreceive, the up transmission power of the signal in the uplink is alsobecome impossible to control. At this time, in the base station, amongsignals in uplink, error of judgment of the down control instruction canbe caused frequently, and also, it becomes possible that the userinformation cannot receive accurately. Even in such case, a conditionwhere communication between the base station and the mobile station isinterrupted, is continued.

On the other hand, in the cellular system, when the mobile station movesbetween cells, there is a soft hand-over technology for switchingchannels between the cells with simultaneously setting the channels witha plurality of the base stations in the vicinity of the boundary betweenthe cells. This technology is important in the cellular system employingthe code division multiplexing system.

Transmission power control in uplink during execution of soft hand-overis important for enabling reception of all up control instructions ofall base stations where the propagation loss in uplink potentiallybecomes minimum.

Therefore, a method for controlling the transmission power of thedownlink to equalize the desired wave power from respective basestations in the mobile station, can be considered. However, in thismethod, since the base station having large propagation loss to themobile station sets the down transmission power to be largecorrespondingly to increase interference wave and whereby to reducecapacity of the downlink. As a method for restricting reduction of thecapacity of the downlink, there is a method for controlling the downtransmission power of respective base stations to be equal to eachother.

In this method, a reception power of the up control instruction from thebase station having small propagation loss to the mobile station isgreater than the reception power of the up control instruction from thebase station having large propagation loss to the mobile station. When adifference of the propagation losses is large, probability of receptionfailure of the up control instruction from the base station having largepropagation loss becomes high. In such case, the transmission power inthe uplink is mainly controlled by up control instruction from the basestation having small propagation loss. Therefore, no significant problemwill be arisen. On the other hand, when the difference of thepropagation losses is small, it is important to control the uptransmission power according to both base stations. In such case, sincerespective up control instructions can be received at substantiallyequal power, probability of accurately receiving both up controlinstructions becomes high. Accordingly, for transmission power controlof the uplink, all up control instructions from the base stations whichpotentially have minimum propagation loss of the uplink can be received.

On the other hand, during execution of soft hand-over, when large andsmall of the propagation loss from the mobile station to respective basestations is switched at high speed due to fading fluctuation or othercause, the base station having the minimum propagation loss performstransmission at any moment even without switching of the base stationsto perform transmission to the mobile station at high speed. At thistime, unless the down transmission power of the base stations are equalto each other, reception quality can be increased or decreased uponswitching of the base station having the minimum propagation loss toeasily cause degradation of the reception quality. However, when downtransmission power of respective base stations are equal to each other,the reception quality can be maintained substantially constant even whenthe base stations having the minimum propagation loss is switched toimprove reception quality by diversity effect.

In such transmission power control in downlink, the mobile stationmeasures the reception quality of the downlink to compare with thetarget control value to transmit the down control instruction forreducing the down transmission power for the base station when thereception quality is higher than the target control value, and totransmit the down control instruction for increasing the downtransmission power for the base station when the reception quality islower than the target control value. During execution of soft hand-over,the down control instruction transmitted from the mobile station isreceived by a plurality of base stations. Then, respective base stationscontrols the down transmission power to increase or decrease accordingto the down control instruction. Accordingly, if the initial values ofthe down transmission power of respective base stations are mutuallyequal to each other, similar increase or decrease is repeated. If noerror is contained in reception of down control instruction, downtransmission power can be controlled with maintaining equal condition.

However, in this method, in the base station where the propagation lossto the mobile station becomes minimum, down control instruction from themobile station can be received in substantially accurate. However, inthe base station having relatively large propagation loss intransmission from the mobile station, reception of down controlinstruction from the mobile station can be frequently failed for smalltransmission power of the down control instruction. Accordingly, itbecomes impossible maintain the down transmission powers of respectivebase stations equal to each other.

Therefore, during execution of the soft hand-over, a transmission powercontrol method in the cellular communication system, in whichsubstantially equal power can be transmitted from respective each basestation even if error is caused in reception of the down controlinstruction in respective base stations, and whereby high channelcapacity can be attained, has been proposed in Japanese UnexaminedPatent Publication No. Heisei 11-340910.

FIG. 6 schematically shows the construction of the cellularcommunication system. In FIG. 6, service area is divided into first andsecond cells 11 and 12. In the first and second cells 11 and 12, a firstbase station (#1) 21 and a second base station (#2) 22 are respectivelyarranged. Also, first and second mobile stations 61 and 62 are presentin the first and second cells 11 and 12. The first and second basestations 21 and 22 are connected to a common control station 71. Thecommon control station 71 is connected to a communication network (notshown) constituted of other control station. It should be noted thatwhile not illustrated, the cellular communication system includes otherlarge number of base stations, and in each cell, large number of mobilestations are present.

The first and second base stations 21 and 22 transmit first and secondpilot signals 31 and 32 at respectively given transmission power. Eachmobile station 61, 62 has SIR (a ratio of desired wave and aninterference power) measuring equipment for measuring a power of thepilot signal for respectively measuring reception power of the first andsecond pilot signals 31 and 32. The mobile station switches themeasuring equipment of the pilot signal in a short period per slot (timeslot) as shown in FIG. 7 and measures the pilot signals of a pluralityof base station once per frame. In the example of FIG. 7, six slots arepresent within one frame and permit measurement of the pilot signalsfrom the six base stations at the maximum. In FIG. 6, the referencenumerals 41, 41 a, 41 b, 42 denote signals in downlink and 51, 52 denotesignals in uplink.

Next, discussion will be given for the transmission power control fordownlink in the cellular communication system shown in FIG. 6 withreference to FIG. 8. FIG. 8 is a flowchart showing operation of the basestation for determining the down transmission power in the downlink inresponse to the down control instruction from the mobile station duringsoft hand-over. Here, the down transmission power P is expressed by adecibel value.

When the base station initiates soft hand-over with the mobile station,if the base station in question is the primary base station which hasbeen transmitting to the mobile station before, the down transmissionpower P maintains the preceding value of the transmission power to themobile station. On the other hand, if the base station is an auxiliarybase station newly starting transmission to the mobile station, the downtransmission power P is set at an initial value P0. The primary stationand the auxiliary station are notified a frame number to initiate softhand-over from the control station 71. The initial value P0 may be anarbitrary value falling within a control range of the down transmissionpower.

At first, when a transmission power balance control message between aplurality of base stations arrives from the control station 71, the basestation resets a frame counter I=0 (step S201). The frame counter I isincremented by 1 per frame (step S202). Here, the down controlinstruction (TPC: Transmission Power Control) is notified from themobile station at a given interval. When the newly notified down controlinstruction is present (step S203) and the down control instructiondesignates increasing of the power (step S204), the down transmissionpower P is increased for a predetermined value ΔP (step S205), and whenthe down control instruction designates decreasing of the power, thetransmission power P in the downlink is decreased for the predeterminedvalue ΔP (step S206).

The foregoing processes S203 to S206 are repeated for frame numberNperiod as a predetermined balance adjusting period. After expiration ofthe predetermined balance adjusting period (step S207), namely when INperiod is established, a difference (C−P) between a predeterminedreference power (referred to as target value or reference value) C andthe down transmission power P before updating, is multiplied with acoefficient (1−r) to integrate the down transmission power P (stepS208).

P=P+(1−r)(C−P)

The coefficient r is a predetermined value within a range greater thanor equal to 0 and less than 1. On the other hand, C is an intermediatepower between the maximum power Pmax and the minimum power Pmin of thetransmission power P.

If the updated transmission power is greater than the maximum powerPmax, the down transmission power P is set at the maximum power Pmax(steps S209, S210). When the updated transmission power P is smallerthan the minimum power Pmin, the down transmission power P is set at theminimum power Pmin (steps S211, S212). Then, the process is repeatedfrom the step S202.

In this method, upon timing of initiation of the soft hand-over, sincethe initial values of the down transmission power of the primary basestation and the auxiliary base station are different, there is adifference |P1−P2| between the down transmission power P1 of the primarybase station and the down transmission power P2 of the auxiliary basestation. On the other hand, upon failure of reception of the downcontrol instruction in one or more base stations, the difference |P1−P2|of these transmission powers P1 and P2 can be increased. However, in aportion of control through steps S203 to S206, namely a portion forincreasing and decreasing the down transmission power by the downcontrol instruction from the mobile station, respective base stationsreceive the same down control instruction. Therefore, respective basestations do not fail reception of the down control instruction, the downtransmission power P1 and P2 are increased or decreased in similarmanner so as not to vary the difference |P1−P2| of these downtransmission powers P1 and P2.

On the other hand, at the same time, per frame number of I=Nperiod, theprimary base station and the auxiliary base station simultaneouslyupdate the down transmission powers P1 and P2 as P1+(1−r)(C−P1),P2+(1−r)(C−P2). Therefore, the difference |P1−P2| of the downtransmission powers P1 and P2 becomes r|P1−P2|. Thus, the difference|P1−P2| of the down transmission power becomes r times per the periodNperiod. Since the coefficient r is smaller than 1, the difference ofthe control amount is decreased in geometric manner to be converged to 0unless the difference |P1−P2| of the down transmission powers isincreased due to reception error of the new down control instruction. Onthe other hand, even if the difference |P1−P2| of the down transmissionpower is increased due to occurrence of reception error of the new downcontrol instruction, the difference |P1−P2| can be decreased.Accordingly, even by failure of reception of the down controlinstruction, the transmission powers Pi (i=1, 2) in the downlink can beadjusted to substantially equal value between the base stations withoutdirect exchange of information concerning the down transmission powerbetween the base stations.

Namely, after increasing or decreasing the down transmission power bythe control at steps S203 to S206, the difference of the downtransmission power of a plurality of base stations can be decreased(balance adjustment), and thus the down transmission power is updated tobe closer to the reference power C determined in common for a pluralityof base stations.

As set forth above, during execution of the soft hand-over by the mobilestation, up control instruction of the transmission power control of theuplink is transmitted at substantially equal power between the basestations from each base station to the mobile station, Therefore, whenthe propagation losses from respective base stations to the mobilestations are substantially the same, when the propagation loss in theuplink can be minimum in any base station all up control instructionscan be received in the mobile station. Accordingly, the mobile stationcan control the up transmission power so that the desired wave powerwill not become excessive for any base station.

On the other hand, during execution of the soft hand-over, even if largeand small relationship of the propagation losses from the mobile stationand respective base stations is switched at high speed due to fadingfluctuation or the like, owing to diversity effect to maintain thereception quality substantially constant, the reception quality in themobile station can be further improved. By controlling the uptransmission power so that the desired wave power will not becomeexcessive, channel capacity of the uplink can be increased. On the otherhand, if the reception quality in the mobile station can be improved bydiversity effect, the channel capacity of the downlink at constantreception quality, can be increased.

As set forth above, in each base station, the transmission power isdecreased for an adjusting amount in the balance adjusting period forthe transmission power. The adjusting amount is derived as apredetermined ratio of the difference between the transmission power atstarting timing of the adjusting period and the reference value C. Thismanner is illustrated in FIG. 9A. In the drawings of FIGS. 9A and 9B,Pbali (i=1, 2) is the power amount to be adjusted, and T1, T2 and T3 areadjusting timings. It should be noted that the drawing shows the widthof Pbali with taking r=0.

Since the transmission power in each base station is increased ordecreased according to the same transmission power control instruction(TPC bit) from the mobile station, if reception error is not containedin the transmission power control instruction, the transmission power ofthe base station can be increased or decreased in similar manner. Atthis time, if the start timing of the adjusting period is the sametiming at respective base stations, when the transmission power of oneof two base stations is large (P1>P2), the difference Pbal between thetransmission power at the start timing of the adjusting period and thereference value C is also large in comparison with that of other basestation (Pbal1>Pbal2), the transmission power (P1) of one of two basestations is decreased significantly during the adjusting period. As setforth, the base station having large transmission power is significantlydecreased the transmission power to reduce the difference of thetransmission power between the base stations to effect balanceadjustment.

However, as shown in FIG. 9B, when the start timing of the adjustingperiod is difference between the base stations such as T1 and T1′, sincethe transmission power according to the transmission power controlinstruction is constantly varied, if the transmission power of one oftwo base stations becomes greater than the other base station (P1>P2),the adjustment start timing TI of the former base station is a momentwhere the transmission power is relatively small, and the adjustmentstart timing of later base station is a moment where the transmissionpower is relatively large, the difference between the transmission powerat start timing of the adjusting period and the reference C becomeslarge in the later base station than the former base station(Pbal1<Pbal2) to significantly reduce the transmission power of theadjusting period. Therefore, the difference of the transmission powersof the base stations becomes large to cause difficulty in establishingbalance of the power. As a result, equalization of the transmissionpowers between the base stations cannot be achieved to decrease channelcapacity.

As set forth above, the phenomenon where the start timings of theadjusting periods are different such as T1 and T1′, is caused by thefluctuation of arrival timings of the control messages for transmissionpower balance adjustment to respective base stations 21 and 22 from thecontrol station 71 due to fluctuation of transmission delay between thecontrol station and the base station. The reception timings of thecontrol messages for conventional power balance adjustment shown in FIG.2A is shown in the case where the reception timings are differentbetween the base stations. In FIG. 2A, Nperiod=2 is taken as balanceadjusting period and eight frame number of 0 to 7 are taken to repeat.As set forth above, in the prior art, a difference of the receptiontimings of the power balance control messages is constantly continuedsubsequently. Therefore, calculation timings of Pbal between the basestations are shifted constantly. As shown in FIG. 9B, reversal of Pbal1and Pbal2 can be caused.

BRIEF SUMMARY OF THE INVENTION

It is an object of the present invention to provide a transmission powercontrol system, a method therefor, a base station and a control station,and a storage medium recording a control program therefor, which canestablish synchronization by matching adjustment start timings whilerepeating adjustment periods even when start timings of transmissionpower balance adjustment are different due to fluctuation oftransmission delay of control message from the control station to basestation, and can increase circuit capacity by establishing balance oftransmission powers between the base stations.

According to the first aspect of the present invention, a transmissionpower control system in a cellular communication system including aplurality of cells, a plurality of base stations respectively arrangedin respective of the plurality of cells, mobile stations located withinthe cells, and control station provided in common for the plurality ofbase stations and transmitting control instruction for balanceadjustment of transmission power to respective of the mobile stationsfrom the base stations, wherein the base station comprises control meansfor controlling initiation of a balance adjustment period for performingthe balance adjustment from a frame number determined on the basis offrame number of the balance adjustment period.

In the preferred construction, assuming that a frame number oftransmission frame to the mobile station is CFN and the balanceadjustment period is Nperiod frame, the control means is in responsiveto reception of the control instruction to perform initiation control ofthe balance adjustment period from the frame of the frame number CFN tobe mod (CFN, m×Nperiod)=L (wherein, m is natural number, L is 0 ornatural number smaller than m×Nperiod common to all base stations).

On the other hand, assuming that a frame number of transmission frame tothe mobile station is CFN and the balance adjustment period is Nperiodframe, the control means is responsive to reception of the controlinstruction to perform initiation control of the balance adjustmentperiod from a frame where a number at the first digit as expressing theCFN by m×Nperiod base number (wherein, m is natural number) becomes apredetermined value.

Furthermore, assuming that a frame number of transmission frame to themobile station is CFN and the balance adjustment period is Nperiodframe, the control means is responsive to reception of the controlinstruction to perform initiation control of the balance adjustmentperiod from a frame where the CFN becomes m×Nperiod+L (wherein m is 0 ornatural number and L is 0 or natural number common to all base stations.

Also, the control station may include means for selecting the Nperiod asa value satisfying a relationship of k×Nperiod=CFNmax (k is integer)assuming that a frame number of transmission frame to the mobile stationis CFN, the balance adjustment period is Nperiod frame, minimum value ofthe CFN is 1, maximum value is CFNmax or minimum value is 0 and maximumvalue is CFNmax−1, and control means of each of the base station mayinitiate control of the balance adjustment period from a frame to bem×Nperiod+L (wherein m is 0 or natural number and L is 0 or naturalnumber common to all base stations).

Also, assuming that a frame number of transmission frame to the mobilestation is CFN, the balance adjustment period is Nperiod frame, thecontrol means selects the Nperiod as a value satisfying a relationshipof k×Nperiod=CFNmax (k is integer) when minimum value of the CFN is 1,maximum value is CFNmax or minimum value and maximum value is CFNmax−1,to initiate control of the balance adjustment period from a frame to bem×Nperiod+L (wherein m is 0 or natural number and L is 0 or naturalnumber common to all base stations). The control means may set anadjustment amount in the balance adjustment at a value of predeterminedratio to a difference between the transmission power upon initiation ofthe balance adjustment period and a reference value.

Furthermore, assuming that the CFN is incremented by one in every frameto be reset to 0 when the CFN exceeds a predetermined number, thecontrol means is responsive to reception of the control instruction tocontrol the balance adjustment starting at a frame with CFN moduloNperiod equal to 0, and repeating for every Nperiod frame, andrestarting at a frame with CFN=0.

According to the second aspect of the present invention, a transmissionpower control method in a cellular communication system including aplurality of cells, a plurality of base stations respectively arrangedin respective of the plurality of cells, mobile stations located withinthe cells, and control station provided in common for the plurality ofbase stations and transmitting control instruction for balanceadjustment of transmission power to respective of the mobile stationsfrom the base stations, wherein the method comprises a control step ofcontrolling initiation of a balance adjustment period for performing thebalance adjustment from a frame number determined on the basis of framenumber of the balance adjustment period, in each base station.

Then, assuming that a frame number of transmission frame to the mobilestation is CFN and the balance adjustment period is Nperiod frame, thecontrol step includes a step of initiating control of the balanceadjustment period from the frame of the frame number CFN to be mod (CFN,m×Nperiod)=L (wherein, m is natural number, L is or natural numbersmaller than m×Nperiod common to all base stations) in response toreception of the control instruction.

Also, assuming that a frame number of transmission frame to the mobilestation is CFN and the balance adjustment period is Nperiod frame, thecontrol step is responsive to reception of the control instruction toperform initiation control of the balance adjustment period from a framewhere a number at the first digit as expressing the CFN by m×Nperiodbase number (wherein, m is natural number) becomes a predeterminedvalue.

Furthermore, assuming that a frame number of transmission frame to themobile station is CFN and the balance adjustment period is Nperiodframe, the control step includes a step responsive to reception of thecontrol instruction to perform initiation control of the balanceadjustment period from a frame where the CFN becomes m×Nperiod+L(wherein m is 0 or natural number and L is 0 or natural number common toall base stations.

The control station performs a step of selecting the Nperiod as a valuesatisfying a relationship of k×Nperiod CFNmax (k is integer) assumingthat a frame number of transmission frame to the mobile station is CFN,the balance adjustment period is Nperiod frame, minimum value of the CFNis 1, maximum value is CFNmax or minimum value is 0 and maximum value isCFNmax−1, and control step in each of the base station initiate controlof the balance adjustment period from a frame to be m×Nperiod+L (whereinm is 0 or natural number and L is 0 or natural number common to all basestations).

On the other hand, assuming that a frame number of transmission frame tothe mobile station is CFN, the balance adjustment period is Nperiodframe, the control step selects the Nperiod as a value satisfying arelationship of k×Nperiod CFNmax (k is integer) when minimum value ofthe CFN is 1, maximum value is CFNmax or minimum value is 0 and maximumvalue is CFNmax−1, to initiate control of the balance adjustment periodfrom a frame to be m×Nperiod+L (wherein m is 0 or natural number and Lis 0 or natural number common to all base stations). The control stepsets an adjustment amount in the balance adjustment at a value ofpredetermined ratio to a difference between the transmission power uponinitiation of the balance adjustment period and a reference value.

Also, assuming that the CFN is incremented by one in every frame to bereset to 0 when the CFN exceeds a predetermined number, the control stepis responsive to reception of the control instruction to control thebalance adjustment starting at a frame with CFN modulo Nperiod equal to0, and repeating for every Nperiod frame, and restarting at a frame withCFN=0.

According to the third aspect of the present invention, a base stationin a cellular communication system including a plurality of cells, aplurality of the base stations respectively arranged in respective ofthe plurality of cells, mobile stations located within the cells, andcontrol station provided in common for the plurality of base stationsand transmitting control instruction for balance adjustment oftransmission power to respective of the mobile stations from the basestations, the base station comprises: control means for controllinginitiation of a balance adjustment period for performing the balanceadjustment from a frame number determined on the basis of frame numberof the balance adjustment period.

Also, assuming that a frame number of transmission frame to the mobilestation is CFN and the balance adjustment period is Nperiod frame, thecontrol means initiation control of the balance adjustment period fromthe frame of the frame number CFN to be mod (CFN, m×Nperiod)=L (wherein,m is natural number, L is or natural number smaller than m×Nperiodcommon to all base stations).

Furthermore, assuming that a frame number of transmission frame to themobile station is CFN and the balance adjustment period is Nperiodframe, the control means is responsive to reception of the controlinstruction to perform initiation control of the balance adjustmentperiod from a frame where a number at the first digit as expressing theCFN by m×Nperiod base number (wherein, m is natural number) becomes apredetermined value.

Furthermore, assuming that a frame number of transmission flame to themobile station is CFN and the balance adjustment period is Nperiodframe, the control means is responsive to reception of the controlinstruction to perform initiation control of the balance adjustmentperiod from a frame where the CFN becomes m×Nperiod+L (wherein m is 0 ornatural number and L is 0 or natural number common to all base stations.

Assuming that a frame number of transmission frame to the mobile stationis CFN and the balance adjustment period is Nperiod frame, the controlmeans resumes the balance adjustment period from a frame to bem×Nperiod+L when the frame number is varied from the maximum value to aminimum value or from the minimum value to the maximum value indiscontinuous manner.

Also, assuming that a frame number of transmission frame to the mobilestation is CFN, the balance adjustment period is Nperiod frame, thecontrol means selects the Nperiod as a value satisfying a relationshipof k×Nperiod=CFNmax (k is integer) when minimum value of the CFN is 1,maximum value is CFNmax or minimum value and maximum value is CFNmax−1,to initiate control of the balance adjustment period from a frame to bem×Nperiod+L (wherein m is 0 or natural number and L is 0 or naturalnumber common to all base stations). The control means sets anadjustment amount in the balance adjustment at a value of predeterminedratio to a difference between the transmission power upon initiation ofthe balance adjustment period and a reference value.

Furthermore, assuming that the CFN is incremented by one in every frameto be reset to 0 when the CFN exceeds a predetermined number, thecontrol means is responsive to reception of the control instruction tocontrol the balance adjustment starting at a frame with CFN moduloNperiod equal to 0, and repeating for every Nperiod frame, andrestarting at a frame with CFN=0.

According to the fourth aspect of the invention, a control station in acellular communication system including a plurality of cells, aplurality of base stations respectively arranged in respective of theplurality of cells, mobile stations located within the cells, andcontrol station provided in common for the plurality of base stationsand transmitting control instruction for balance adjustment oftransmission power to respective of the mobile stations from the basestations, each of the base station initiate control of a balanceadjustment period from a frame to be m×Nperiod+L (wherein m is 0 ornatural number and L is 0 or natural number common to all base stations,Nperiod is a period for performing the balance adjustment), the controlstation comprising means for selecting the Nperiod as a value satisfyinga relationship of k×Nperiod=CFNmax (k is integer) assuming that a framenumber of transmission frame to the mobile station is CFN, the balanceadjustment period is Nperiod frame, minimum value of the CFN is 1,maximum value is CFNmax or minimum value is 0 and maximum value isCFNmax−1.

According to the fifth aspect of the present invention, a storage mediumstoring a transmission power control method in a cellular communicationsystem including a plurality of cells, a plurality of base stationsrespectively arranged in respective of the plurality of cells, mobilestations located within the cells, and control station provided incommon for the plurality of base stations and transmitting controlinstruction for balance adjustment of transmission power to respectiveof the mobile stations from the base stations, wherein the controlprogram comprises a control step of controlling initiation of a balanceadjustment period for performing the balance adjustment from a framenumber determined on the basis of frame number of the balance adjustmentperiod, in each base station.

According to the sixth aspect of the present invention, a storage mediumstoring a transmission power control method in a cellular communicationsystem including a plurality of cells, a plurality of base stationsrespectively arranged in respective of the plurality of cells, mobilestations located within the cells, and control station provided incommon for the plurality of base stations and transmitting controlinstruction for balance adjustment of transmission power to respectiveof the mobile stations from the base stations, each of the base stationinitiate control of a balance adjustment period from a frame to bem×Nperiod+L (wherein m is 0 or natural number and L is 0 or naturalnumber common to all base stations, Nperiod is a period for performingthe balance adjustment), the control program comprising step ofselecting the Nperiod as a value satisfying a relationship ofk×Nperiod=CFNmax (k is integer) assuming that a frame number oftransmission frame to the mobile station is CFN, the balance adjustmentperiod is Nperiod frame, minimum value of the CFN is 1, maximum value isCFNmax or minimum value is 0 and maximum value is CFNmax−1.

In the operation, upon soft hand-over of certain mobile station with aplurality of base stations, when balance adjustment of the transmissionpower from a plurality of base stations to the mobile station, balanceadjustment period for performing balance adjustment in each base stationis initiated at the frame number determined on the basis of number offrames in the balance adjustment period. By this, even when thereception timing of the balance control message from the control stationis shifted due to fluctuation of transmission delay, synchronization ofbalance calculation timing for balance adjustment can be establishedbetween the base stations during repletion of balance adjustment periodto enable accurate balance of the transmission power between the basestations.

On the other hand, when the balance control message is received in eachbase station before and after discontinuous variation of the framenumber of the transmission frames from the maximum value to the minimumvalue (or from the minimum value to the maximum value), timing ofbalance adjustment can be shifted due to relationship between the periodof the balance adjustment and total number of frames. However, byresuming balance adjustment period from the frame defined by the samerule as the rule determining the frame initiating the balance adjustmentperiod, the frame number to be candidate of initiation of the balanceadjustment period is held unchanged even when the frame number isrepeated returning from the maximum value to the minimum value.Accordingly, synchronization is established between the base stations inthe balance calculation timing, balance of transmission power can beaccurately established between the base stations.

On the other hand, a frame number of transmission frame to the mobilestation is CFN, the balance adjustment period is Nperiod frame, byselecting the Nperiod as a value satisfying a relationship ofk×Nperiod=CFNmax (k is integer), the frame number to be candidate ofinitiation of the balance adjustment period is held unchanged even whenthe balance control message is received in each base station before andafter discontinuous variation of the frame number of the transmissionframes from the maximum value to the minimum value (or from the minimumvalue to the maximum value). Accordingly, synchronization is establishedbetween the base stations in the balance calculation timing, balance oftransmission power can be accurately established between the basestations.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be understood more fully from the detaileddescription given hereinafter and from the accompanying drawings of thepreferred embodiment of the present invention, which, however, shouldnot be taken to be limitative to the invention, but are for explanationand understanding only. In the drawings:

FIG. 1 is a schematic block diagram showing a construction of anembodiment of a base station according to the present invention;

FIGS. 2A and 213 are timing charts showing calculation timing of atransmission power balance according to the present invention, shown ascomparison with the prior art;

FIG. 3 is a flowchart showing one embodiment of operation of the basestation according to the present invention, which is illustrated for thecase where CFN max is a integer multiple of Nperiod;

FIG. 4 is an illustration showing an example of operation when CFNmax isnot integer multiple of Nperiod;

FIG. 5 is a flowchart showing another embodiment of operation of thebase station according to the present invention, which is illustratedfor the case where CFN max is not necessarily a integer multiple ofNperiod;

FIG. 6 is an illustration showing a system construction to which thepresent invention is applied;

FIG. 7 is a chart showing a frame structure in the present invention;

FIG. 8 is a flowchart showing operation of the base station in theconventional system; and

FIGS. 9A and 9B are charts showing the cases where satisfactory balanceadjustment of the transmission power cannot be achieved when the powerbalance control message from control station reaches respective basestations at different timing due to fluctuation of transmission delay.

DETAILED DESCRIPTION OF THE INVENTION

The present invention will be discussed hereinafter in detail in termsof the preferred embodiment of the present invention with reference tothe accompanying drawings. In the following description, numerousspecific details are set forth in order to provide a thoroughunderstanding of the present invention. It will be obvious, however, tothose skilled in the art that the present invention may be practicedwithout these specific details

FIG. 1 is a schematic block diagram showing a construction of thepreferred embodiment of a base station according to the presentinvention. It should be noted that a system construction is the same asthat illustrated in FIG. 6. On the other hand, a frame structure ofdownlink from the first base station (#1) 21 and the second base station(#2) 22 to the mobile station 51 is the same as the example shown inFIG. 7. Between the base stations, frame number to be transmitted at thesame time is the same.

Referring to FIG. 1, the base station includes an antenna 201, atransmission and reception common portion 202, a reception circuit 203performing reception process of a received signal and outputting thereceived signal to a terminal 207, a SIR measuring portion 204performing SIR measurement of downlink, a transmission power controlportion 205 performing control of a transmission power with reference tothe result of SIR measurement or the like, and a transmission circuit206 superimposing transmitting signal from a terminal 208 and SIRmeasurement result signal and controlling amplification depending uponcontrol from the transmission power control portion 205. On the otherhand, in order to perform operation control for respective portions, CPU(control unit) 209 and read-only storage medium (ROM) 210 preliminarilystoring program for operation control of CPU are included.

The present invention prevents occurrence of the transmission powers ofthe base stations falling out of balance for increasing of differencetherebetween due to shifting of timings, such as T1 and T1′ of the powerbalance control messages from the control station 71 at the first basestation #1 and the second base station #2, as shown in FIG. 9B.Therefore, as shown in FIG. 2B, the adjustment start timings of powerbalance between the base stations become the same to establishsynchronization with each other.

In the example shown in FIG. 2B, there is shown an example where themessage is consisted of eight frames of frame numbers CFN of 0 to 7(total number of the frame (number) is CFNmax, CFNmax−1=7), the messageof eight frames is repeated, and the adjusting period is set as Nperiod2.

Generally expressing, three modes are considered. At first, in the firstmode, balance adjustment period is controlled to start at a frame of theframe number CFN which is expressed by:

mod(CFN,m×Nperiod)=L

wherein m is natural number, L is 0 or natural number smaller thanNperiod and common to all base stations. Namely, at the frame of theframe number to have remainder “L” as dividing CFN by (m×Nperiod),balance adjustment is initiated. Subsequently, balance adjustment isperformed at every Nperiod. In the example of FIG. 2B, it corresponds tom=1 and L=0. In FIGS. 2A and 2B, a calculation timing of Pbal is shownas leading end of the frame. However, in practice, the Pbal calculationtiming may be a predetermined timing (e.g. (S)th slot) of the frame.

As second mode, when the frame number CFN is expressed by m×Nperiod basenumber (m is natural number), balance adjustment is initiated from theframe where the number of the first digit becomes a predetermined value.Subsequently, balance adjustment is performed at every Nperiod. In theexample shown in FIG. 2B, this corresponds to the case where m=1 and thepredetermined value=0.

As the third mode, the balance adjustment is initiated from the framewhere the frame number CFN becomes m×Nperiod+L, wherein m is 0 ornatural number and L is 0 or natural number common to all base stations.In the example shown in FIG. 2B, this corresponds to the case where m=1and L=0.

FIG. 3 is a flowchart showing operation of the base station in theforegoing respective modes. In response to arrival (reception) of thepower balance control message from the control station, the controloperation shown in FIG. 3 is initiated. At first, a current frame numberCFN is obtained (step S11), and a frame counter (not particularly shown)I is set at I=mod (CFN, Nperiod) (step S12). Then, Pbal=(1−r) (C−P)shown in FIG. 9 is reset to 0 (step S13). It should be noted that FIG. 9is illustrated as a level where the reference value C becomes smallerthan the transmission powers P1 and P2 of respective base stations. Insuch case, it becomes Pbal (1−r) (P−C). However, in the shown embodimentdiscussion will be shown in the case where the reference value C is setto be greater than the transmission powers P1 and P2 of respective basestations.

Next, a slot counter (not particularly illustrated) J is reset to J=0(step S14). Then, the system is placed in waiting state for TPC bit(step S15). In response to reception of the TPC bit, when the TPC bit ispower increasing instruction (step S16), the transmission power P iscontrolled to increase for a predetermined amount S1 (step S17).Conversely, when the TPC bit is power decreasing instruction, thetransmission power P is controlled to decrease for the predeterminedamount S1 (step S18). When Pbal is greater than a predetermined value S2(step S19), the transmission power P is controlled to increase for thepredetermined amount 82 (step S20) and Pbal is controlled to decreasefor the predetermined amount S2 (step S21).

At step S19, when Pbal is smaller than the predetermined amount S2,comparison of Pbal and −S2 is performed (step S22). If Pbal is smallerthan −S2, a process of P−S2 is performed (step S23), and in conjunctiontherewith, Pbal is controlled to increase for the predetermined amountS2 (step S24). After steps S21 and S24 or when answer at step S22 is“NO”, the slot counter is incremented by 1 (step S25).

The foregoing process of steps S15 to S25 is repeated for number ofslots Nslot consisting one frame (step S26). By repeating for Nslottimes to be J=Nslot, the frame counter I is incremented by 1. Then,process transit to the process for the next frame (step S28). At thistime, until I becomes equal to Nperiod, the process through foregoingsteps S14 to S27 is repeated.

When I=Nperiod is established, adjustment of Pbal is initiated. Namely,Pbal (1−r) (C−P) is calculated (step S29), and resetting of the framecounter I=0 is performed (step S30). Them, process is returned to stepS14 against start transmission power control from the first slot J=0 inthe next frame.

Through the foregoing process, control of the transmission power ofrespective base stations in downlink is performed by the TPC bit in eachslot, and in conjunction therewith, synchronization of initiation timingof power balance between the base stations is established withcompensating error of initiation timing due to fluctuation caused bytransmission delay of the power balance control message from the controlstation.

Operational flowchart shown in FIG. 3 is a flowchart which can beestablished only when CFNmax is integer multiple of N period in the casewhere the frame number CFN is 0 to maximum value (CFNmax−1) and totalframe number is repeated in CFNmax. However, when CFNmax is not integermultiple of Nperiod, for example, as shown in FIG. 4, calculation timingof Pbal of the base station #1 is executed per Nperiod 3 afterinitiation from the frame number CFN=4. In the next frames of 0 to 7,the frame number CFN=2 becomes the calculation timing. At this time,when arrival timing of the power balance control message to the basestation #2 is the frame number CFN=1, calculation timing of Pbal becomesthe frame number CFN=4. Then, synchronization of calculation timings ofboth base stations cannot be established to cause a problem.

Therefore, in such case, in the base station #1, the frame number CFN isreset to “0” to restart calculation timing from the frame number ofm×Nperiod+L (m is 0 or natural number, L is 0 or natural number commonto all base stations) for establishing synchronization between the basestations #1 and #2. It should be noted that, in the example of FIG. 4,m=0 and L=1.

As set forth above, the frame number is varied from the maximum value tothe minimum value (or from the minimum value to the maximum value) indiscontinuous manner, synchronization can be established by restartingthe balance control period from the frame determined by the same rule asthe rule determining the frame starting the balance adjustment period.

In such case, operational flowchart of the base station is shown in FIG.5. In the flowchart shown in FIG. 5, the same or equivalent steps withthe flowchart shown in FIG. 3 are shown by the same reference numeralsand redundant discussion for such common steps will be eliminated foravoiding redundancy of disclosure and whereby for maintaining thedisclosure simple enough to facilitate clear understanding of thepresent invention. Therefore, the following discussion will be givenmainly for portions different from FIG. 3. Next to step S27, a framenumber counter CFN is provided and is incremented by 1 (step S31). Then,the value of the frame number counter is checked whether it becomes themaximum value CFNmax or not (step S32). If the result of checking is“YES”, the frame number counter CFN is reset to “0” (step S33). The,process is returned to step S29.

In the discussion for FIGS. 4 and 5, there is shown the case where valueof the frame number counter is ascending order, the same is applicablefor the case of descending order.

In FIG. 5, Pbal is calculated based on the power value P at the end ofthe frame per Nperiod frame including CFN=0. On the other hand, in theflowcharts shown in FIGS. 3 and 5, Pbal is calculated as Pbal=(1−r)(C−P) for updating Pbal per calculation. However, it may be an examplefor integration as Pbal=Pbal+(1−r) (C−P).

By selecting a value where an integer k to establish k×Nperiod=CFNmax asNperiod, the embodiment resetting the foregoing frame number counter CFNto “0” becomes unnecessary, as a matter of course. In this case,selecting Nperiod at a value at which an integer k satisfyingk×Nperiod=CFNmax, is present, may be performed by the base station.However, such selection is typically done by the control station and isnoticed to each base station. Accordingly, in each base station, bystarting balance adjustment at the frame to be m×Nperiod+L,synchronization of calculation timing in both base station can beestablished even when the frame number CFN is varied from the maximumvalue to the minimum value (or conversely returning from the minimumvalue to the maximum value for counting down). For example whenCFNmax=256, Nperiod is selected among 1, 2, 4, 8, 16, 32, 64, 128 and256.

On the other hand, concerning operational flowchart of FIGS. 3 and 5,the process is executed by CPU 209 which reads out the program stored inthe storage medium, such as ROM 210 shown in FIG. 1. While notparticularly illustrated, concerning functional block diagram andoperational flowchart in the control station, by preliminarily storingoperation control program in the storage medium, CPU may read out theprogram for execution to perform operation of transmission of thetransmission power balance control message and selected.

As set forth above, according to the present invention, when receptiontimings of the control signal are different due to fluctuation oftransmission delay of the control signal from the control station to thebase station, even though starting points of the first adjusting periodare different, timing of subsequent balance adjustment is synchronized.By this, balance of the transmission power between the base stations canbe improved to contribute for increasing of channel capacity.

Particularly, in the invention performing resumption control,synchronization of timing of balance adjustment can be established evenwhen a value where k satisfying k×CFNmax does not present is selected asNperiod. Therefore, Nperiod can be selected irrespective of the value ofCFNmax. Therefore, in order to satisfy predetermined demanded referencefor balancing the transmission power between the base stations,frequency of balance adjustment has to be greater than or equal to apredetermined frequency. However, since Nperiod can be selectedirrespective of the value of CFNmax, frequency of balance adjustment canbe made greater than or equal to the predetermined frequency butminimum. Therefore, process of control for establishing synchronizationof timing of balance adjustment can be reduced.

On the other hand, in the present invention for selecting the valuewhere k satisfying k×Nperiod=CFNmax, as Nperiod, resumption controlbecomes unnecessary even when total number of frames is limited.Therefore, process of control for establishing synchronization of timingof balance adjustment can be reduced.

Although the present invention has been illustrated and described withrespect to exemplary embodiment thereof it should be understood by thoseskilled in the art that the foregoing and various other changes,omission and additions may be made therein and thereto, withoutdeparting from the spirit and scope of the present invention. Therefore,the present invention should not be understood as limited to thespecific embodiment set out above but to include all possibleembodiments which can be embodied within a scope encompassed andequivalent thereof with respect to the feature set out in the appendedclaims.

1. A transmission power control method in a cellular communicationsystem including a plurality of cells, a plurality of base stationsrespectively arranged in respective of said plurality of cells, mobilestations located within said cells, and control station provided incommon for said plurality of base stations and transmitting controlinstruction including a balance adjustment period for balance adjustmentof transmission power to respective of said mobile stations from saidbase stations, wherein assuming that a frame number of transmissionframe to said mobile station is CFN and said balance adjustment periodis Nperiod frame, said method comprises a step of adding 1 to said CFNevery frame and resetting said CFN to zero when said CFN exceeds amaximum value, a step of starting said balance adjustment from the frameof the frame number CFN to be mod (CFN, m Nperiod)=0 (m being a naturalnumber) in response to reception of said control instruction, in eachbase station, and step of restarting said balance adjustment from theframe of the frame number CFN to be zero, in each base station.
 2. Abase station in a cellular communication system including a plurality ofcells, a plurality of base stations respectively arranged in respectiveof said plurality of cells, mobile stations located within said cells,and control station provided in common for said plurality of basestations and transmitting control instruction including a balanceadjustment period for balance adjustment of transmission power torespective of said mobile stations from said base stations, whereinassuming that a frame number of transmission frame to said mobilestation is CFN and said balance adjustment period is Nperiod frame, saidbase station comprises means for adding 1 to said CFN every frame andresetting said CFN to zero when said CFN exceeds a maximum value, meansfor starting said balance adjustment from the frame of the frame numberCFN to be mod (CFN, m Nperiod)=0 (m being a natural number) in responseto reception of said control instruction, and means for restarting saidbalance adjustment from the frame of the frame number CFN to be zero. 3.A mobile station in a cellular communication system including aplurality of cells, a plurality of base stations respectively arrangedin respective of said plurality of cells, mobile stations located withinsaid cells, and control station provided in common for said plurality ofbase stations and transmitting control instruction including a balanceadjustment period for balance adjustment of transmission power torespective of said mobile stations from said base stations, whereinassuming that a frame number of transmission frame to said mobilestation is CFN and said balance adjustment period is Nperiod frame, eachbase station comprises means for adding 1 to said CFN every frame andresetting said CFN to zero when said CFN exceeds a maximum value, meansfor starting said balance adjustment from the frame of the frame numberCFN to be mod (CFN, m Nperiod)=0 (m being a natural number) in responseto reception of said control instruction, and means for restarting saidbalance adjustment from the frame of the frame number CFN to be zero;and said mobile station comprising means for transmitting a controlinstruction for controlling said transmission power.
 4. A transmissionpower control system in a cellular communication system including aplurality of cells, a plurality of base stations respectively arrangedin respective of said plurality of cells, mobile stations located withinsaid cells, and control station provided in common for said plurality ofbase stations and transmitting control instruction including a balanceadjustment period for balance adjustment of transmission power torespective of said mobile stations from said base stations, whereinassuming that a frame number of transmission frame to said mobilestation is CFN and said balance adjustment period is Nperiod frame, eachbase station comprises means for adding 1 to said CFN every frame andresetting said CFN to zero when said CFN exceeds a maximum value, meansfor starting said balance adjustment from the frame of the frame numberCFN to be mod (CFN, m Nperiod)=0 (m being a natural number) in responseto reception of said control instruction; and means for restarting saidbalance adjustment from the frame of the frame number CFN to be zero. 5.A storage medium storing a transmission power control program in acellular communication system including a plurality of cells, aplurality of base stations respectively arranged in respective of saidplurality of cells, mobile stations located within said cells, andcontrol station provided in common for said plurality of base stationsand transmitting control instruction including a balance adjustmentperiod for balance adjustment of transmission power to respective ofsaid mobile stations from said base stations, wherein assuming that aframe number of transmission frame to said mobile station is CFN andsaid balance adjustment period is Nperiod frame, said program comprisesa step of adding 1 to said CFN every frame and resetting said CFN tozero when said CFN exceeds a maximum value, a step of starting saidbalance adjustment from the frame of the frame number CFN to be mod(CFN, m Nperiod)=0 (m being a natural number) in response to receptionof said control instruction, in each base station, and a step ofrestarting said balance adjustment from the frame of the frame numberCFN to be zero, in each base station.
 6. The method according to claim1, further comprises a step of controlling initiation of said balanceadjustment period for performing said balance adjustment from a framenumber determined on the basis of frame number of the balance adjustmentperiod.
 7. The base station according to claim 2, further comprisesmeans for controlling initiation of said balance adjustment period forperforming said balance adjustment from a frame number determined on thebasis of frame number of the balance adjustment period.
 8. The mobilestation according to claim 3, said each base station further comprisesmeans for controlling initiation of said balance adjustment period forperforming said balance adjustment from a frame number determined on thebasis of frame number of the balance adjustment period.
 9. Thetransmission power control system according to claim 4, said each basestation further comprises means for controlling initiation of saidbalance adjustment period for performing said balance adjustment from aframe number determined on the basis of frame number of the balanceadjustment period.
 10. The program according to claim 5, furthercomprises a step of controlling initiation of said balance adjustmentperiod for performing said balance adjustment from a frame numberdetermined on the basis of frame number of the balance adjustmentperiod.